Clinical analytical procedures are increasingly becoming automated owing to technological advances, such that, for example, multiple items can be assayed by several different reagents simultaneously in one device. The extent of clinical monitoring items in the area of hemostasis and thrombosis does not end merely with blood coagulation time, but ramifies into quantitating the factors in the clotting/fibrinolytic system, and to quantitating fibrin degradation products; and it is now possible to make these measurements with a single device.
Automated hematological analyzers accordingly are able to investigate any hemostatic disorder, as well as risk of thrombosis. That is, by performing multiple assays on hematological samples, "coagulation profiles" are produced, from which bleeding disorders as well as the potential for pathological formation of cardiovascular blood clots (thrombi) can be evaluated.
Coagulation assays are performed in the hematological analyzer by mixing test reagents into hematological samples in reaction tubes and monitoring for diagnostic change; typically the time to onset of clotting in the sample is measured.
In human blood coagulation, in the pathway common to both the intrinsic (plasma-mediated) and extrinsic (tissue-mediated) pathways, the protease Factor X (Stuart Factor) is activated, which in turn activates prothrombin, by cleaving it to yield thrombin. Thrombin in turn cleaves fibrinogen to yield clot-forming fibrin.
Tissue factor (TF), released from tissues exposed to plasma from a ruptured blood vessel, can activate Factor X directly. Accordingly, a laboratory blood coagulation test known as the prothrombin time (PT) assay can be conducted to evaluate the extrinsic and common pathways. A test reagent containing tissue factor (also called thromboplastin) is added to a plasma sample, activating Factor X via the extrinsic route. The time to clot formation in the sample following the addition of the thromboplastin reagent is measured as the PT.
An evaluation of the integrity of the intrinsic pathway is by assaying for Factor VIII (antihemophilic factor), which for example can test for hemophilia. Factor VIII functions with other coagulation cascade proteases and calcium ions to activate Factor X. Accordingly, a Factor VIII reagent may be added to a plasma sample and, as with the PT test, the time to clotting monitored, except that therein the intrinsic pathway is evaluated.
On the other hand, clot-forming fibrin, the protein end product of blood coagulation, must eventually be degraded, which occurs through factors having fibrinolytic functions.
Plasmin is the activated enzyme responsible for fibrin degradation in the fibrinolytic system, and is derived from converted plasminogen in the blood. Plasmin activity is in turn regulated by .alpha..sub.2 -antiplasmin, a principal inhibitor of fibrinolysis. Monitoring plasmin levels can accordingly indicate hemostatic integrity or thrombosis.
By the same token, antiplasmin levels can be assayed to evaluate fibrinolytic function. For example, by adding a plasmin-containing reagent to a hematological sample in a reaction tube, antiplasmin can then be quantitated.
Furthermore, the blood coagulation system must be regulated to prevent massive formation of thrombi. Blood consequently contains natural clotting cascade inhibitors.
Protein C is a coagulation inhibitor, functioning to lock the activity of activated Factor VIII, as well as another clotting factor. At the same time, Protein C inactivates an inhibitor of tissue plasminogen activator (tPA is secreted primarily by endothelial cells and activates plasmin), thus enhancing fibrinolytic activity.
Levels of Protein C can be assayed by adding to a sample a chromogenic synthetic peptide substrate that is cleaved in the presence of the reaction between a protease (Factor VIII, for example) and its inhibitor (Protein C, for example). Cleavage of the synthetic substrate produces a chromogenic change that can be quantitated photometrically.
The intrinsic clotting pathway by definition can be activated solely by elements within the blood itself, when intrinsic Factor XII (Hageman Factor) comes into contact with and is bound by a negatively charged surface (thus the pathway can be triggered in vitro). The time to coagulation via this mechanism is referred to as the "partial thromboplastin time," in relation to the time to coagulation required when the extrinsic pathway is initiated via thromboplastin.
The intrinsic clotting system can be screened generally for abnormalities by the activated partial thromboplastin time (aPTT) assay. This test is also used to monitor the anticoagulant effect of heparin treatment. Heparin occurs naturally in the basophils of blood leukocytes, but is prepared as a commercial product from animal sources and administered therapeutically. Heparin accelerates the activity of Antithrombin III (ATIII). ATIII is the major inhibitor of the enzymes of the clotting cascade, binding to some half-dozen proteases, including factors X and XII and thrombin. Antithrombin III acting with co-factor heparin functions immediately to inhibit coagulation.
The aPTT assay is conducted by adding a test reagent containing a Factor XII activator to a platelet-poor plasma sample. Time to clotting is evaluative of adequate levels of the intrinsic coagulation factors.
Antithrombin III levels can be assayed by employing a synthetic peptide substrate as with the assay for Protein C levels described above.
In the above-described automated hematological analyzers, measuring reagents and test samples are taken up by means of a pipette-like aspirating device (sampling probe) and ejected into reaction vessels.
Ideally, pipette devices used herein would be provided according to use, as it were, for each particular assaying reagent or each particular sample. However, due to cost and apparatus size limitations, a single pipette device is utilized in common. Herein, if the pipette device is not cleaned sufficiently the problem of "carry-over" occurs, in which prior-remaining matter is mixed in with next-aspirated reagents, exerting an influence on the analytical results.
In hemostasis and thrombosis assays, methods include clotting time and chromogenic substrate tests, as described above, as well as immunoassays. Among the reagents employed in these assaying methods are many that have enzymatic activity, or in the case of chromogenic substrates, that contain proteins or peptides. Because enzymes, and proteins and peptides generally, tend to become adsorbed on the pipette device, carry-over problems are liable to arise with the use of such reagents, making sufficient cleaning of the pipette device necessary. Conventionally the pipette device has been cleaned with a cleansing fluid containing a hypochlorite substance.
Nevertheless, there are situations in which using the above-noted cleansing fluid insufficiently cleans the pipette device in the automated analyzer. This has been particularly so with the foregoing plasmin-containing anti-plasmin assaying reagents, and PT reagents containing recombinant tissue factor. Moreover, increasing the concentration of the hypochlorite substance is not satisfactory, since this damages the tubes and other fluid components, or else brings about effects due to the residual hypochlorite substance itself. Further, the undesirability of a drop in processing capacity (throughput) of the automated analyzer due to the cleaning process therefore demands instantaneous cleansing.